Improved clinch knot is handy for tyring lures to the line. Surgeon's knot for joining lines, nail knot for joining fly line to leader. Palomar knot is another handy one. There are actually lots of handy knots. Go online and find some guides and just sit down some cold winter evening and play around.
When I was taking my firefighting courses, I had to learn about a dozen knots, and since then I've gotten interested enough in ropework to learn a few more that are handy for camping and rigging. Slipcing ropes in kind of fun too- like working a puzzle.